Published in June 2020 in the Las Vegas Optic.
We all know what riparian vegetation is – don’t we? It’s the bosque. It grows along and near a riverbank and is essential to the good health of any river. Rivers, including our own Gallinas, can deteriorate or undergo changes that adversely affect their health; but if their riparian vegetation is in place and thriving, rivers will recover from whatever afflicts them and likewise thrive. A crucial part of this vegetation is willow especially, and also cottonwood – the woody vegetation. Willows and cottonwoods have been largely scorned by us – the unwitting public – as too water hungry. Those two trees should, instead, be appreciated and preserved.
Owing to their distinctive characteristics, willows especially and also cottonwoods have astonishing capabilities that do much to maintain the health of the river. Their root systems, their trunks, and their leaves and branches each play a role in the river’s continued good health. Together, the whole tree helps preserve the shape of the river, maintain water quality and regulate water quantity; contribute to drought and flood mitigation and climate control, and create fish and wildlife habitat.
Willows’ root system, for example, is dense and far reaching. The roots as well as the branches slow rain water run-off and direct it downward into the soil. The soil takes over and filters out toxins and other impurities. After that, the water may remain to recharge ground water or slowly return to the river, cleaner than it was before.
Think of an August monsoon – a heavy, though short, downpour. Where does all that water go? Some of it races down our streets and alleys and into storm drains. Near the River Walk, however, are several industry sites with asphalt yards. The rain coming down on those naturally heads downhill. If that flow is not redirected, it and all the contaminants it has picked up from the yards will go straight into the river. Willows to the rescue.
The same root systems hold a river together. When willows grow on either side of a stream their roots form a kind of hammock beneath the bed and prevent the bank and bed from eroding. As banks erode, they crumble and fall into the stream leaving behind a diminished bank that is further away from the stream. It can make a stream too wide and too shallow. The water slows down and the sun has a lot more time to heat things up. Warm water holds less oxygen than does cool water; warm water evaporates more rapidly than does cool water. The slow flow also drops sediment that otherwise would continue to travel downstream. The sediment fills up pools and the pools disappear as do the trout that need them. Bed erosion causes a different and likewise detrimental set of conditions. When the river bed erodes, it becomes too deep and straight – like a channel or a trough. When that happens, the water flows faster and faster and is quickly lost to the area.
These types of erosion contribute to an unhealthy stream. When willows grow on the banks, erosion is prevented. The stream keeps its shape – its meanders, riffles, and pools – and that means it flows not too fast and not too slowly. Willows foster the growth and development of macro-invertebrates. These are such critters as stone flies, caddis flies, dragonflies, may flies; all of which provide food for trout. The willow canopy (branches and leaves) provides food for macro-invertebrates.
The canopy also produces cooling shade to reduce evaporation and then traps much of the evaporation that still occurs to create a cool and moist environment that prevents yet further evaporation. The resulting micro-climate is heaven to flies, wildlife, and people, and keeps the water cool too.
In 2019, volunteers with the Gallinas River Park Collaborative (GRPC) undertook a difficult but satisfying task. The volunteers planted three hundred willows and forty cottonwoods along the Gallinas, a few hundred yards south of Bridge Street. They, along with riparian plant life already present, are to be the chief protectors and sustainers of the river. It was certainly cause for consternation when the GRPC discovered that many of the new plants had been damaged – snapped off near ground level. It’s not possible to know who was responsible or why the damage was done. We can help to reduce the chance of it happening again by spreading the word that doing harm to the riparian vegetation ultimately harms the river and us.
Without the willows to maintain a cool and moist environment, to prevent erosion and evaporation, and to enable the cleaning and storing of rainwater, the river’s riparian ecosystem will dry up. The trout will disappear as will all of the wildlife that depend on the river and its bosque. It is true that willows need and use water – they are not desert plants – but considering all they give us in return, our Gallinas environment will happily support them.